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Introduction to Stoichiometry

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What is Stoichiometry?

Stoichiometry is at the heart of the production of many things you use in
your daily life. Soap, tires, fertilizer, gasoline, deodorant, and chocolate
bars are just a few commodities you use that are chemically engineered, or
produced through chemical reactions. Chemically engineered commodities all rely
on stoichiometry for their production.

But what is stoichiometry? Stoichiometry is the calculation of quantities in
chemical equations. Given a chemical reaction, stoichiometry tells us what
quantity of each reactant we need in order to get enough of our desired product.
Because of its real-life applications in chemical engineering as well as
research, stoichiometry is one of the most important and fundamental topics in
chemistry.

Introduction to the Mole

Which weighs more, 100 pounds of feathers or 100 pounds of bowling balls?
You've probably heard this riddle before. Obviously they both weigh the same
since I told you I have 100 pounds of each. But if I have 100 pounds of bowling
balls and 100 pounds of feathers, do I have more feathers or more bowling balls?
The quantities of feathers and bowling balls would not be equal. An individual
feather weighs a lot less than a bowling ball. It would take only about 10
bowling balls to get 100 pounds whereas it would take a LOT more feathers.

When you measure quantities in moles, however, the situation is exactly opposite
from when you measure according to weight. A mole is defined as the
amount of a substance. More specifically, there are
6.02×1023
particles in a mole of substance. Therefore, if you had 1 mole
of feathers and 1 mole of bowling balls, you would have
6.02×1023
feathers and
6.02×1023
bowling balls. Now suppose you were asked
the question, "Which weighs more, 100 moles of feathers or 100 moles of bowling
balls?" The answer this time would be the bowling balls. Although there is an
equal number of both feathers and bowling balls, an individual bowling ball
weighs much more than an individual feather, and so an equal number of bowling
balls would weigh more than an equal number of feathers.

Now, let's return to the number
6.02×1023
. This number is known as
Avogadro's number and you should definitely commit it to memory. You are
probably wondering why it's so large, and it does indeed look intimidating
without the exponential notation:

6.02×1023 = 60, 200, 000, 000, 000, 000, 000, 000, 000

Although you will never have a mole of bowling balls, you will soon be
calculating moles of compounds, molecules, atoms, and ions. These
representative particles are extremely and incredibly small. That is why there
are so many particles in a mole of substance. When you appreciate just how
small these particles are,
6.02×1023
stops seeming like such a
crazy number.